The podcast is now available here. Greg also provides links to two shows featuring Mac pulled from the Radio Misterioso archives. Note: The link shown is a "permalink" which, for whatever obscure reason does not contain the featured podcast... Currently, that can only be found on Radio Misterioso's main page at the end of the October 18th post...)
"That’s right, this week’s show features a special segment during hour three where the Gralien crew pays tribute to one of the great minds to have come and gone in the field of the esoteric: Mac Tonnies, the late author of The Cryptoterrestrials and After the Martian Apocalypse. He will be missed, but in dedicating a tribute to him on the show, it is my hope that we’ll help ensure that his work will run no risk of being forgotten."
Meanwhile, it has come to my attention that another radio tribute to Mac took place on the 18th of this month. Micah Hanks is joined by Mike Clelland and Dr. Maxim Kammerer - who explores Mac's Cryptoterrestrial hypothesis in this post - in a podcast which can be found here. (Hat-tip to RPJ!)